Archived 2020 topic: Barbuda Warbler (Setophaga subita): request for information

BirdLife species factsheet for Barbuda Warbler

Barbuda Warbler (Setophaga subita) is endemic to Barbuda. It inhabits most habitat types on the island, but prefers xeric scrub and dry forest, particularly with higher canopy (Mahabir 2018, Diamond 2020). The population size has been placed in the band 600-1,700 mature individuals.

The species appears to tolerate a substantial level of habitat degradation and has successfully adapted to cattle and goat grazing within its range (Diamond 2020). It is however feared that continuing loss and degradation of habitat may now start triggering population declines (J. Daltry per D. Diaz in litt. 2019).

Barbuda Warbler has been considered Near Threatened, approaching the threshold for listing as threatened under Criterion D1+2 (BirdLife International 2020). However, a review of available information on the population size and uncertainty surrounding the population trend suggest that the species may warrant a change in Red List status. Therefore, we have fully reviewed the species here against all criteria.

Criterion A – Thepopulation trend is difficult to quantify. On one hand, large parts of the natural vegetation of Barbuda have been degrading through cattle and goat grazing for over a century; yet the species seems to be well adapted to this disturbance and it is not thought that it may cause a severe population decline (Diamond 2020). Furthermore, it appears that hurricane Irma, which hit Barbuda in 2017, did not have a severe impact on the population size either (Gerbracht 2017). On the other hand, anecdotal evidence suggests that levels of habitat degradation have increased considerably, so that the species is now starting to decline (J. Daltry per D. Diaz in litt. 2019). Therefore tentatively, it is suspected that the species is undergoing a slow decline. The timeframe relevant for Criterion A is three generation lengths or ten years, whichever is longer. One generation length for Barbuda Warbler is 2.3 years (Bird et al. 2020)*; hence the rate of population decline needs to be assessed over ten years. Given the resilience of Barbuda Warbler to habitat loss and degradation, it is unlikely that the rate of decline meets the threshold for listing as threatened under Criterion A (≥30% over ten years); nevertheless, in order to assess the species against this criterion, we ask for recent information regarding the population trend.

Criterion B – The species’s range is confined to one island, where it is thought to be relatively evenly distributed (see records on eBird; eBird 2020). EOO (Extent of Occurrence) and maximum Area of Occupancy (AOO), as calculated by a 4 km2 grid over the area of mapped range, both amount to 268 km2.  This value meets the thresholds for Endangered (EOO < 5,000 km2; AOO < 500 km2) under Criterion B1+2. However, in order to be listed under this criterion, at least two further conditions have to be met.

Barbuda Warbler is found throughout its range and forms one subpopulation. As such, it is not severely fragmented sensu IUCN (IUCN Standards and Petitions Committee 2019). Threats to the species include habitat degradation through goat grazing, habitat loss through clearing and potentially the impact of hurricanes. However, there is currently no evidence that any of these threats can extirpate large parts of the population within the next ten years, given that the species has shown a high level of resilience in the past. The number of locations**, as defined by the most serious plausible threat, is therefore not thought to be restricted to ≤ 10, and the species does not meet condition a.

Natural vegetation on Barbuda is lost and degraded though land clearance, goat and cattle grazing and illegal fires (EAG 2009). Based on this information, we can infer an ongoing declines in habitat quality. Barbuda Warbler thus meets condition b(iii). There is no evidence of extreme fluctuations in the distribution range or population size, and condition c is not met.

Overall, even though EOO and AOO are small, the species does not meet enough conditions to be listed as threatened. Therefore, Barbuda Warbler may be listed as Near Threatened, approaching the threshold for listing as threatened under Criterion B1b(iii)+2b(iii). We are asking for up-to-date information regarding the threats the species is facing and their potential impacts on the population size in order to accurately quantify the number of locations* of occurrence.

Criterion C – The population is estimated to number 600-1,700 mature individuals. This meets the threshold for listing as Endangered under Criterion C. However, in order to be listed under this criterion, further conditions must be met.

The species is precautionarily suspected to undergo a decline. A suspected decline, however, precludes a listing as threatened under Criterion C; so the species can at most be listed as Near Threatened under this criterion. All individuals are thought to belong to the same subpopulation. Therefore, Barbuda Warbler qualifies as Near Threatened, approaching the threshold for listing as threatened under Criterion C2a(ii).

Criterion D – The population size meets the threshold for listing as Vulnerable under Criterion D1. The AOO is too large to meet or approach the threshold for listing as threatened; it therefore depends on the number of locations** of occurrence whether the species additionally qualifies for listing as threatened under Criterion D2. Based on current data, the number of locations* is likely large, but we are asking for recent information on threats the species is facing and their potential impacts on the population size.

Criterion E – To the best of our knowledge, there has been no quantitative analysis of extinction risk conducted for this species. Therefore, it cannot be assessed against this criterion.

Hence, based on currently available information it appears that the only criterion where the species meets the threshold for listing as threatened is Criterion D1. Therefore, up-to-date information is urgently sought regarding the population trend of Barbuda Warbler as well as the intensity of threats the species is facing.

Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’ Red List status. Therefore, please make sure your comments are relevant to the species’ Red List status and the information requested. By submitting a comment, you confirm that you agree to the Comment Policy.

*Bird generation lengths are estimated using the methodology of Bird et al. (2020), as applied to parameter values updated for use in each IUCN Red List for birds reassessment cycle. Values used for the current assessment are available on request. We encourage people to contact us with additional or improved values for the following parameters; adult survival (true survival accounting for dispersal derived from an apparently stable population); mean age at first breeding; and maximum longevity (i.e. the biological maximum, hence values from captive individuals are acceptable).

**The term ‘location’ refers to a distinct area in which a single threatening event can rapidly affect all individuals of the taxon present, with the size of the location depending on the area covered by the threatening event. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat (IUCN 2001, 2012).

An information booklet on the Red List Categories and Criteria can be downloaded here and the Red List Criteria Summary Sheet can be downloaded here. Detailed guidance on IUCN Red List terms and definitions and the application of the Red List Categories and Criteria can be downloaded here.

References

Bird, J. P.; Martin, R.; Akçakaya, H. R.; Gilroy, J.; Burfield, I. J.; Garnett, S.; Symes, A.; Taylor, J.; Šekercioğlu, Ç.; Butchart, S. H. M. 2020. Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology online first view.

BirdLife International. 2020. Species factsheet: Setophaga subita. http://www.birdlife.org (Accessed 07 April 2020).

Diamond, A. W. 2020. Barbuda Warbler (Setophaga subita), version 1.0. In: Schulenberg, T. S. (ed.). Birds of the World. Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.barwar.01 (Accessed 07 April 2020).

eBird. 2020. eBird: An online database of bird distribution and abundance [web application]. eBird, Cornell Lab of Ornithology, Ithaca, NY, USA. http://www.ebird.org (Accessed 07 April 2020).

EAG. 2009. Loss of Biodiversity. https://www.eagantigua.org/page551.html (Accessed 07 April 2020).

Gerbracht, J. 2017. Barbuda after Irma: A devastated landscape, a proud people – and a resilient bird. https://www.birdscaribbean.org/2017/11/barbuda-after-irma-a-devastated-landscape-a-proud-people-and-a-resilient-bird/ (07 April 2020).

IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K.

IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1. Second edition. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K. www.iucnredlist.org/technical-documents/categories-and-criteria.

IUCN Standards and Petitions Committee. 2019. Guidelines for using the IUCN Red List Categories and Criteria. Version 14. http://www.iucnredlist.org/documents/RedListGuidelines.pdf.

Mahabir, K. 2018. Influence of habitat on the occurrence of the endemic Barbuda Warbler (Setophaga subita) and resident Yellow Warbler (S. petechia). PhD thesis. University of New Brunswick, Canada.

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3 Responses to Archived 2020 topic: Barbuda Warbler (Setophaga subita): request for information

  1. Red List Team (BirdLife International) says:

    The window for consultation is now closed. We will analyse and interpret the new information and post a preliminary decision on this species’s Red List status on this page in early July.

    Thank you,
    BirdLife Red List Team

  2. Red List Team (BirdLife International) says:

    Preliminary proposal

    It is suspected that the species is starting to undergo a population decline. However, uncertainties and a lack of information surrounding the rate of decline and the threats that the species is facing does not allow a detailed assessment against Criteria A and B.

    Based on available information, our preliminary proposal for the 2020 Red List would be to list Barbuda Warbler as Vulnerable under Criterion D1.

    There is now a period for further comments until the final deadline in mid-July, after which the recommended categorisations will be put forward to IUCN.

    Please note that we will then only post final recommended categorisations on forum discussions where these differ from those in the initial proposal.

    The final 2020 Red List categories will be published on the BirdLife and IUCN websites in December 2020/January 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  3. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN

    The final categorisation for this species has not changed. Barbuda Warbler is recommended to be listed as Vulnerable under Criterion D1.

    Many thanks for everyone who contributed to the 2020 GTB Forum process. The final 2020 Red List categories will be published on the BirdLife and IUCN websites in December 2020/January 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN.

Comments are closed.